PSXII-29 Utilizing coproducts as an alternative to forage in adapting feedlot cattle to finishing diets affects the ruminal microbiome

Abstract

Abstract The objective was to determine the interaction of replacing forage with coproducts and the number of step-up diets when adapting feedlot cattle to a finishing diet on the ruminal microbiome. Simmental × Angus and Angus steers (n = 24; 234 ± 38 kg) were blocked by initial body weight (BW) and allotted to 8 pens as a subset of a larger group. Pens were randomly assigned to 1 of 2 dietary treatments: 1) decreasing coproduct (CO; soybean hulls and modified wet distillers grains) inclusion while increasing dry-rolled corn over 36 d or 2) decreasing forage (FO; alfalfa and grass hay) inclusion while increasing dry-rolled corn over 36 d. Pens were fed either 5 (5S) or 2 (2S) step-up diets for each dietary treatment during the 36 d adaptation period in a 2 × 2 factorial design. Steers were fed a common finishing diet for the remainder of the trial (34 d). The ruminal microbiome was evaluated on d 36 and 70. Alpha diversity was greatest (P < 0.01) for FO/2S steers on d 36. A diet × day effect (P = 0.02) was observed for beta diversity as the microbial community was more similar (P < 0.01) between d 36 and 70 for steers fed CO compared with FO. Relative abundance of Bacteroidetes was greater (P = 0.03) for 2S steers compared with 5S steers. Prevotellaceae tended to be greater (P = 0.07) in 2S steers compared with 5S steers. Lactobacillaceae was greater (P < 0.01) on d 36 than d 70. Limited observed day effects for individual taxa suggest the microbiome was well adapted by treatments for the finishing diet on d 36. Greater coproduct inclusion in adaptation diets may alter the ruminal bacterial community to be more similar to the community while feeding high levels of dry-rolled corn.